|Region||Fukushima, Tochigi, Ibaraki|
|• elevation||1,022 m (3,353 ft)|
|Mouth||Pacific Ocean (at Hitachi and Tokai)|
|Length||124 km (77 mi)|
|Basin size||1,490 km2 (580 sq mi)|
|• location||Sakakibashi (榊橋)|
|• average||27.1[a] m3/s (960 cu ft/s)|
Kuji River (Japanese: 久慈川, Hepburn: Kuji-gawa) is a river in Fukushima Prefecture, Tochigi Prefecture and Ibaraki Prefecture, Japan. It rises at the northern slope of Mount Yamizo, where the border of these three prefectures is located, and flows into Pacific Ocean at Hitachi and Tokai in Ibaraki Prefecture. It has a length of 124 kilometers (77 mi) and a drainage area of 1,490 square kilometers (580 sq mi), and is designated as a Class A river.
The name of Kuji is thought to have been named after whale (kujira in Japanese). Hitachi no kuni fudoki, one of the existent Fudoki, says, "There were a hill that resembled a whale (kujira). Then the emperor named the land Kuji." The river is known for ayu fishing, and in 2006 it had the second largest catch of ayu in Japan after Naka River, which is also located in Ibaraki Prefecture. The fishing weir (梁 yana) for tourists is installed along the river in Daigo. Famous Fukuroda Falls are located on Taki River (滝川 Takigawa), which is one of its tributary rivers. On midwinter a phenomenon called shiga can be observed in the river. Shiga is a phenomenon in which frazil ice that is generated at the bottom floats on the surface. Distribution of freshwater fish like salvelinus and masu salmon captured in Fukushima Prefecture had been restricted after Fukushima Daiichi nuclear disaster, though in Kuji River the restriction was gradually removed.
Kuji River originates from the northern slope of Mount Yamizo, where the border of Fukushima Prefecture, Tochigi Prefecture and Ibaraki Prefecture is located. It initially flows to the northeast in Tanagura, Fukushima and then changes the flow direction to the sounth in the town. The dividing ridges of Abukuma River and Kuji River are relatively low, and it is considered that Kuji River captured the course of Abukuma River in the past. It flows along a narrow plain between Yamizo Mountainsand Abukuma Mountains and into Ibaraki Prefecture. In Ibaraki Prefecture it flows through Daigo, Hitachiomiya and flows finally into Pacific Ocean at the border of Hitachi and Tokai. While the mainstream of the river flows through Fukushima Prefecture and Ibaraki Prefecture, some tributaries flow through Otawara in Tochigi Prefecture (former Kurobane), which is located in the southwest of Mt.Yamizo.
The approximately 80% of the basin consists of mountains and hills, and the rest consists of plateaus and plains. In the downstream basin there is Naka Plateau (那珂台地) between Naka River and Kuji River, which is a fluvial terrace formed by the erosion and deposition by the two rivers.
In the basin there are five cities, five towns and two villages, which are listed below. As of 1995[update] the population of the basin is approximately 200,000.